LCDs are widely used in various modern information products, such as notebooks, personal digital assistants (PDAs), video cameras and the like. The wide usage of the LCD is due to its advantages such as portability, low power consumption, and low radiation. LCDs are passive optical devices. Therefore in general, a backlight module is needed to provide sufficient illumination for an LCD panel of the LCD, so as to enable the LCD panel to display images.
Generally, a backlight module includes a light source and a light guide plate (LGP). The LGP is for guiding light beams emitted by the light source, so that the light beams transmit to a predetermined display area. The light source can for example be a cold cathode fluorescent lamp (CCFL) or one or more light emitting diodes (LEDs). A typical LED is small, and light beams emitted by an LED are more focused. Therefore the LED is more suitable for a small sized product, such as an LCD used in a mobile phone, a portable media player, a PDA, or the like.
In general, it is difficult to manufacture a white light emitting diode (WLED) that can emit white light beams with high purity. Typically, light beams emitted by a WLED are slightly yellowish. That is, the light beams are mostly white but also partly yellow. These white-yellowish light beams are liable to reduce the display quality of the LCD. One means employed to convert the white-yellowish light beams to pure white light beams is to use an LGP that has a plurality of colored particles incorporated therein. This solution utilizes principles of colored light mixing to achieve white output light having high purity.
FIG. 5 is an isometric view of a conventional backlight module. The backlight module 10 includes a light guide plate (LGP) 13 and a plurality of light sources 12. The LGP 13 is made by injection molding, and includes a top light emitting surface 132, a bottom surface 133, a light incident surface 131 adjacent to the light emitting surface 132 and the bottom surface 133, and a plurality of embedded colored particles 130. The colored particles 130 are typically blue particles, which are sprayed into a molten LGP preform during the injection molding process. Each of the light sources 12 is a white light emitting diode (WLED). The light sources 12 are disposed adjacent to the light incident surface 131 of the LGP 13.
Light beams emitting from the light sources 12 are transmitted into the LGP 13 via the light incident surface 131, with the light beams being white-yellowish. In the LGP 13, some of the white-yellowish light beams are scattered by the colored particles 130, and converted to blue light beams. The blue light beams mix with other white-yellowish light beams that are not scattered, and accordingly white light beams having high purity are generated. The white light beams emit from the light emitting surface 132 of the LGP 13, and enable an LCD employing the backlight module 10 to display high quality images.
The backlight module 10 solves the need to provide pure white light beams. However, the material of the colored particles 130 is different from that of the LGP 13. Therefore when the colored particles 130 are sprayed into the molten LGP preform, the colored particles 130 block cross-linking of molecular structures of the material of the LGP preform. Thus the structural integrity of the formed LGP 13 is weakened.
It is, therefore, desired to provide a backlight module and an LCD employing the backlight module which can overcome the above-described deficiencies.